Method for efficient cold recovery in o2-h2 combustion turbine power generation system

ABSTRACT

A method of efficient cold recovery from a liquid hydrogen stream includes warming a cold liquid hydrogen stream by indirect heat exchange with a cold feed air stream in an ASU sub-cooler, thereby producing a warmed liquid hydrogen stream. Wherein at least a portion of the cool inlet air stream is introduced into a cold booster, thereby producing the compressed cool feed air stream. Wherein at least a first portion of the further cooled feed air stream is introduced into an expander, thereby producing an expanded feed air stream. Wherein a second portion of the further cooled feed air stream is further cooled, thereby producing the cold feed air stream. And, wherein the liquid oxygen stream has a first molar mass flow rate, and the cold liquid hydrogen stream has a second molar flow rate that is between 1.5 and 2.5 times the first molar mass flow rate.

BACKGROUND

Hydrocarbon based fuels are currently used to produce energy, in particular electrical energy, throughout the world. The downside of burning hydrocarbons is the production of unwanted pollutants. Most of these unwanted pollutants are the result of undesirable side reactions, or of the incomplete burning, of the hydrocarbon fuel.

One emerging alternative is to burn hydrogen gas as the fuel. Theoretically, a combustion process utilizing relatively pure hydrogen gas may be performed in the presence of relatively pure oxygen gas. Depending on the nature and amount of impurities in the feed gases, this combustion would result almost entirely in the production of water. It is thus a very environmentally friendly alternative to burning hydrocarbons fuels.

Additionally, an optimally designed oxygen-hydrogen combustion turbine, for example, can theoretically operate at an overall combustion efficiency that is 5%-7.5% greater than a hydrocarbon fueled combustion turbine, depending on the combustion temperature.

There are, however, additional considerations that must be taken into account. For example, pure hydrogen burning in the presence of pure oxygen results in a much higher combustion chamber temperature. Often, this temperature is near the limits of current metallurgy. As hydrogen is a very explosive gas, internal seals, leaking and explosion safety are also of paramount importance is such a plant.

Currently, such oxygen-hydrogen combustion turbines are typically being operated by being blended with natural gas. But, as the designs, and in particular the metallurgy advances, it is easy to foresee pure oxygen-hydrogen combustion turbines operating in the near future.

As discussed above, the hydrogen and oxygen are introduced into the combustion chamber in gaseous form. A local air separation unit, or oxygen pipeline, can easily provide the oxygen in non-cryogenic, gaseous phase. However, in most cases, the hydrogen will be transported to the facility in cryogenic liquid form. In which case, a significant amount of energy is then required to bring this cryogenic liquid hydrogen to near-ambient, gaseous form.

If some effort is undertaken, this energy may be utilized, or integrated, within the overall power plant. In this case, this energy may be considered to be “cold heat” or “cold energy”. As used herein, the term “cold heat” is defined as the useful recovery of refrigeration during exploitation of a cryogenic liquid.

The idea of utilizing this “cold heat” from the vaporization of the liquid hydrogen in a power plant is discussed in “Feasibility Study for Oxygen-Hydrogen Combustion Turbine Generation System” by Toshiichi Matsumoto, presented on Nov. 26, 2019 by The Institute of Applied Energy. In this paper, Matsumoto discusses that one aim of his research is to “improve the efficiency as a total system by combining utilization of cold heat of liquefied hydrogen”. However, this paper never actually discusses how this cold heat may be effectively utilized.

Therefore, there is presently a need in the industry to incorporate the cold heat of vaporizing liquid hydrogen to improve the overall efficiency of an oxygen-hydrogen combustion power plant.

SUMMARY

A method of efficient cold recovery from a liquid hydrogen stream is provided. The method includes warming a cold liquid hydrogen stream by indirect heat exchange with a cold feed air stream in an ASU sub-cooler, thereby producing a warmed liquid hydrogen stream. The method includes further heating the warmed liquid hydrogen stream and a liquid oxygen stream by indirect heat exchange with an inlet air stream, and a compressed cool feed air stream, in at least one main heat exchanger, thereby producing a cool inlet air stream, a further cooled feed air stream, the cold feed air stream the compressed cool feed air stream, a gaseous hydrogen stream and a gaseous oxygen stream. Wherein at least a portion of the cool inlet air stream is introduced into a cold booster, thereby producing the compressed cool feed air stream. Wherein at least a first portion of the further cooled feed air stream is introduced into an expander, thereby producing an expanded feed air stream, Wherein a second portion of the further cooled feed air stream is further cooled, thereby producing the cold feed air stream. And, wherein the liquid oxygen stream has a first molar mass flow rate, and the cold liquid hydrogen stream has a second molar flow rate that is between 1.5 and 2.5 times the first molar mass flow rate.

BRIEF DESCRIPTION OF THE FIGURES

For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

FIG. 1 is a schematic representation of one embodiment of the present invention.

FIG. 1a is a schematic representation of another embodiment of the present invention.

FIG. 1b is a schematic representation of another embodiment of the present invention.

FIG. 2 is a schematic representation of another embodiment of the present invention.

FIG. 3 is a schematic representation of another embodiment of the present invention.

FIG. 3a is a schematic representation of another embodiment of the present invention.

FIG. 3b is a schematic representation of another embodiment of the present invention.

FIG. 4 is a schematic representation of another embodiment of the present invention.

FIG. 4a is a schematic representation of another embodiment of the present invention.

FIG. 4b is a schematic representation of another embodiment of the present invention.

FIG. 5 is a schematic representation of another embodiment of the present invention.

FIG. 5a is a schematic representation of another embodiment of the present invention.

FIG. 5b is a schematic representation of another embodiment of the present invention.

ELEMENT NUMBERS

-   -   101=liquid hydrogen stream     -   102=cold liquid hydrogen stream     -   103=cold feed air stream     -   104=air separation unit sub-cooler     -   105=warmed hydrogen stream (out of air separation unit         sub-cooler)     -   106=liquid oxygen stream     -   107=inlet air stream     -   108=compressed cool feed air stream     -   109=main heat exchanger     -   110=cool inlet air stream     -   111=further cooled feed air stream     -   112=gaseous hydrogen stream     -   113=gaseous oxygen stream     -   114=cold booster     -   115=first branch (of further cooled feed air stream)     -   116=expander     -   117=expanded feed air stream     -   118=second branch (of further cooled feed air stream)     -   119=air separation unit column     -   120=liquid nitrogen {from HP column)     -   121=liquid nitrogen {LP column)     -   122=liquid nitrogen export stream     -   123=liquid hydrogen heat exchanger     -   124=first part (of inlet air stream)     -   125=second part (of inlet air stream)     -   126=first cool inlet air stream     -   127=second cool inlet air stream     -   128=first fraction (of compressed cool feed air stream)     -   129=second fraction (of compressed cool feed air stream)     -   130=third portion (of further cooled feed air stream)     -   131=fourth portion (of further cooled feed air stream)     -   132=combined stream (of first portion and third portion of         further cooled feed     -   air stream)     -   133=first portion (of cold feed air stream)     -   134=second portion (of cold feed air stream)     -   135=third portion (of cold feed air stream)     -   136=first expanded feed air stream     -   137=second expanded feed air stream     -   138=combined expanded feed air stream     -   139=second cold booster     -   140=second expander     -   141=first section (of further cooled feed air stream)     -   142=second section (of further cooled feed air stream)     -   201=first heat flow profile     -   202=second heat flow profile     -   203=third heat flow profile     -   204=fourth heat flow profile     -   205=fifth heat flow profile

DESCRIPTION OF PREFERRED EMBODIMENTS

Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

Turning to FIG. 1, a method of efficient cold recovery from a liquid hydrogen stream 101 is provided. The liquid hydrogen stream 101 is pressurized in a liquid hydrogen pump, thus producing a cold liquid hydrogen stream 102. The cold liquid hydrogen stream 102 is then warmed by indirect heat exchange with a cold feed air stream 103 in an ASU sub-cooler 104, thereby producing a warmed hydrogen stream 105. Warmed hydrogen stream 105 may be either liquid phase or gas phase, depending on the degree of warming and the resulting fluid temperature. After being cooled by this indirect heat exchange with the cold liquid hydrogen stream 102, cold feed air stream 103 enters air separation unit column 119.

A liquid oxygen stream is pressurized in a liquid oxygen pump, thus producing a pressurized liquid oxygen stream 106. The warmed hydrogen stream 105 and the liquid oxygen stream 106 are then heated by indirect heat exchange with an inlet air stream 107, and a compressed cool feed air stream 108, in at least one main heat exchanger 109. This exchange produces a cool inlet air stream 110, a further cooled feed air stream 111, the cold feed air stream 103, a gaseous hydrogen stream 112 and a gaseous oxygen stream 113. The gaseous hydrogen stream 112 and the gaseous oxygen stream 113 then leave the system. In one embodiment, the gaseous hydrogen stream 112 and/or the gaseous oxygen stream 113 are then utilized in an oxygen-hydrogen combustion turbine (not shown).

The liquid oxygen stream 106 has a first molar mass flow rate, and the cold liquid hydrogen stream 102 has a second molar flow rate that may be between 1.5 and 2.5 times the first molar mass flow rate. The cold liquid hydrogen stream 102 may have a pressure greater than 13 bare, preferably greater than 40 bare. The liquid oxygen stream 106 may have a pressure greater than 30 tiara.

At least a portion of the cool inlet air stream 110 is introduced into a cold booster 114, thereby producing the compressed cool feed air stream 108. At least a first portion 115 of the further cooled feed air stream 111 is introduced into an expander 116, thereby producing an expanded feed air stream 117. In one embodiment of the present invention, the cod booster 114 and expander 116 are connected by a common drive shaft. In one embodiment, excess power is produced by the combined cold booster 114 and expander 116, which is then used to power an electrical generator (not shown).

A second portion 118 of the further cooled feed air stream 111 is further cooled, thereby producing the cold feed air stream 103.

Turning to FIGS. 1a and 1b , the heat flow profile of specific pathways though the main heat exchanger 109 are defined. A first heat flow profile 201 is defined as further cooled feed air stream 111. This is the portion of the compressed cool feed air stream 108, that has been partially cooled in heat exchanger 109, just prior to first branch 115, being removed. A second heat flow profile 202 is defined as second branch 118 of further cooled feed air stream 111. This is the portion of the compressed cool feed air stream 108, that has been further cooled in heat exchanger 109, after first branch 115, has been removed.

Third heat flow profile 203 is defined as the section of the heat exchanger 109 in which liquid oxygen stream 106 is vaporized and becomes gaseous oxygen stream 113. Fourth heat flow profile 204 is defined as the section of the heat exchanger 109 in which inlet air stream 107 is cooled and becomes cool inlet air stream 110. Fifth heat flow profile 205 is defined as the section of the heat exchanger 109 in which warmed hydrogen stream 105 is heated and becomes gaseous hydrogen stream 112.

As used herein, the term “cold stream” applies to third heat flow profile 203 and fifth heat flow profile 205. As used herein, the term “hot stream” applies to first heat flow profile 201, second heat flow profile 202, and fourth heat flow profile 204.

The sum of the enthalpies at each temperature for the cold streams minus the sum of enthalpies at each temperature for the hot streams divided by the sum of the enthalpies at each temperature for the cold streams is defined as the “irreversible thermal losses” of the heat exchange system.

The instant system is designed such that the irreversible thermal losses are minimized. As used herein, the term “minimized” is defined as meaning less than 10%, preferably less than 7.5%, more preferably less than 5%.

FIG. 2 is one embodiment illustrating, in further detail, air separation column 119 and air separation unit sub-cooler 104. Liquid hydrogen stream 101 passes through air separation unit sub-cooler 104, whereby it exchanges heat indirectly with cold feed air stream 103, and liquid nitrogen stream 120, from the high-pressure column of air separation column 119. After passing through air separation unit sub-cooler 104, cold feed air steam 103 enters the low-pressure column of air separation column 119. After passing through air separation unit sub-cooler 104, liquid nitrogen stream 121 enters the low-pressure column of air separation column 119. In some embodiments, a portion of liquid nitrogen stream 121 exits the system as liquid nitrogen export stream 122.

Turning to FIG. 3, a method of efficient cold recovery from a liquid hydrogen stream 101 is provided. The liquid hydrogen stream 101 is pressurized in a liquid hydrogen pump, thus producing a cold liquid hydrogen stream 102. The cold liquid hydrogen stream 102 is then warmed by indirect heat exchange with a first portion 124 of an inlet air stream 107 in liquid hydrogen heat exchanger 123, thereby producing a first cool inlet air stream 126, and a gaseous hydrogen stream 112.

A liquid oxygen stream is pressurized in a liquid oxygen pump, thus producing a pressurized liquid oxygen stream 106. The liquid oxygen stream 106 is then heated by indirect heat exchange with a second part 125 of inlet air stream 107, and a compressed cool feed air stream 108, in at least one main heat exchanger 109. This exchange produces a second cool inlet air stream 127, a further cooled feed air stream 111, the cold feed air stream the compressed cool feed air stream 103 and a gaseous oxygen stream 113. The gaseous hydrogen stream 112 and the gaseous oxygen stream 113 then leave the system. In one embodiment, the gaseous hydrogen stream 112 and/or the gaseous oxygen stream 113 are then utilized in an oxygen-hydrogen combustion turbine.

The liquid oxygen stream 106 has a first molar mass flow rate, and the cold liquid hydrogen stream 102 has a second molar flow rate that may be between 1.5 and 2.5 times the first molar mass flow rate. The cold liquid hydrogen stream 102 may have a pressure greater than 13 barn, preferably greater than 40 barn. The liquid oxygen stream 106 may have a pressure greater than 30 barn.

At least a portion of second cool inlet air stream 127 is combined with at least a portion of first cool inlet air stream 126 and introduced into a cold booster 114, thereby producing the compressed cool feed air stream 108. At least a first portion 115 of the further cooled feed air stream 111 is introduced into an expander 116, thereby producing an expanded feed air stream 117. In one embodiment of the present invention, the cold booster 114 and expander 116 are connected by a common drive shaft. In one embodiment, excess power is produced by the combined cold booster 114 and expander 116, which is then used to power an electrical generator (not shown).

A second portion 118 of the further cooled feed air stream 111 is further cooled, thereby producing the cold feed air stream 103. Cold feed air stream 103 enters air separation unit column 119.

Turning to FIGS. 3a and 3b , the heat flow profile of specific pathways though the main heat exchanger 109 and liquid oxygen heat exchanger 123 are defined. A first heat flow profile 201 is defined as further cooled feed air stream 111. This is the portion of the compressed cool feed air stream 108, that has been partially cooled in heat exchanger 109, just prior to first branch 115, being removed. A second heat flow profile 202 is defined as second branch 118 of further cooled feed air stream 111. This is the portion of the compressed cool feed air stream 108, that has been further cooled in heat exchanger 109, after first branch 115, has been removed.

Third heat flow profile 203 is defined as the section of the heat exchanger 109 in which liquid oxygen stream 106 is vaporized and becomes gaseous oxygen stream 113. Fourth heat flow profile 204 is defined as both the section of the heat exchanger 109 in which the second part inlet air stream 125 is cooled and becomes second cool inlet air stream 127; and the section of the liquid hydrogen heat exchanger 123 in which the first part inlet air stream 124 is cooled and becomes first cool inlet air stream 126. Fifth heat flow profile 205 is defined as the section of the liquid oxygen heat exchanger 123 in which liquid hydrogen stream 101 is heated and becomes gaseous hydrogen stream 112.

As used herein, the term “cold stream” applies to third heat flow profile 203 and fifth heat flow profile 205. As used herein, the term “hot stream” applies to first heat flow profile 201, second heat flow profile 202, and fourth heat flow profile 204.

The sum of the enthalpies at each temperature for the cold streams minus the sum of enthalpies at each temperature for the hot streams divided by the sum of the enthalpies at each temperature for the cold streams is defined as the “irreversible thermal losses” of the heat exchange system.

The instant system is designed such that the irreversible thermal losses are minimized. As used herein, the term “minimized” is defined as meaning less than 10%, preferably less than 7.5%, more preferably less than 5%.

Turning to FIG. 4, a method of efficient cold recovery from a liquid hydrogen stream 101 is provided. The liquid hydrogen stream 101 is pressurized in a liquid hydrogen pump, thus producing a cold liquid hydrogen stream 102. The cold liquid hydrogen stream 102 is then warmed by indirect heat exchange with a first part 124 of an inlet air stream 107 and a first fraction 128 of compressed cool feed air stream 108 in liquid hydrogen heat exchanger 123, thereby producing a first cool inlet air stream 126, a first branch 115 of a first section of a further cooled feed air stream 141, and a gaseous hydrogen stream 112.

A liquid oxygen stream is pressurized in a liquid oxygen pump, thus producing a pressurized liquid oxygen stream 106. The liquid oxygen stream 106 is then heated by indirect heat exchange with a second part 125 of inlet air stream 107, and a second fraction of compressed cool feed air stream 129, in at least one main heat exchanger 109. This exchange produces a second cool inlet air stream 127, a third portion of further cooled feed air stream 130, and a gaseous oxygen stream 113. The gaseous hydrogen stream 112 and the gaseous oxygen stream 113 then leave the system. In one embodiment, the gaseous hydrogen stream 112 and/or the gaseous oxygen stream 113 are then utilized in an oxygen-hydrogen combustion turbine.

The liquid oxygen stream 106 has a first molar mass flow rate, and the cold liquid hydrogen stream 102 has a second molar flow rate that may be between 1.5 and 2.5 times the first molar mass flow rate. The cold liquid hydrogen stream 102 may have a pressure greater than 13 bara, preferably greater than 40 bara. The liquid oxygen stream 106 may have a pressure greater than 30 bara.

At least a portion of second cool inlet air stream 127 is combined with at least a portion of first cool inlet air stream 126 and introduced into a cold booster 114, thereby producing the compressed cool feed air stream 108. Compressed cool feed air stream is split into a first fraction 128 and a second fraction 129. First fraction 128 is introduced into liquid hydrogen heat exchanger 123, wherein it becomes first fraction of further cooled feed air stream 141, Second fraction 129 is introduced into main heat exchanger 109, wherein it becomes second fraction of further cooled feed air stream 142, At least a first portion 115 of the further cooled feed air stream 141 and at least a third portion 130 of second section of a further cooled feed air stream 142 are combined to form combined stream 132 which is introduced into an expander 116, thereby producing an expanded feed air stream 117. In one embodiment of the present invention, the cold booster 114 and expander 116 are connected by a common drive shaft. In one embodiment, excess power is produced by the combined cold booster 114 and expander 116, which is then used to power an electrical generator (not shown). A second portion 118 of the first fraction of further cooled feed air stream 141 is further cooled, thereby producing the first portion of cold feed air stream 133. A second portion 131 of the second fraction of further cooled feed air stream 142 is further cooled, thereby producing the second portion of cold feed air stream 134. The first portion of cold feed air stream 133 and the second fraction of further cooled feed air stream 134 are combined and the combined stream 135 enters air separation unit column 119.

Turning to FIGS. 4a and 4b , the heat flow profile of specific pathways though the main heat exchanger 109 and liquid oxygen heat exchanger 123 are defined. A first heat flow profile 201 is defined as both first section of a further cooled feed air stream 141 and second section of a further cooled feed air stream 142. First section of a further cooled feed air stream 141 is the portion of the first fraction of compressed cool feed air stream 128, that has been partially cooled in liquid hydrogen heat exchanger 123, just prior to first branch 115, being removed. Second section of a further cooled feed air stream 142 is the portion of the second fraction of compressed cool feed air stream 129, that has been partially cooled in man heat exchanger 109, just prior to third portion 130, being removed.

A second heat flow profile 202 is defined as both second branch 118 of further cooled feed air stream 142 and fourth portion 131 of further cooled feed air stream 141. Second branch 118 is the portion of the first fraction compressed cool feed air stream 128, that has been further cooled in liquid hydrogen heat exchanger 123, after first branch 115, has been removed. Fourth portion 131 is the portion of the second fraction compressed cool feed air stream 129, that has been further cooled in main heat exchanger 109, after third portion 130, has been removed.

Third heat flow profile 203 is defined as the section of the heat exchanger 109 in which liquid oxygen stream 106 is vaporized and becomes gaseous oxygen stream 113. Fourth heat flow profile 204 is defined as both the section of the heat exchanger 109 in which second part of inlet air stream 125 is cooled and becomes second cool inlet air stream 127; and the section of the liquid hydrogen heat exchanger 123 in which first part of inlet air stream 124 is cooled and becomes first cool inlet air stream 126. Fifth heat flow profile 205 is defined as the section of the liquid oxygen heat exchanger 123 in which liquid hydrogen stream 101 is heated and becomes gaseous hydrogen stream 112.

As used herein, the term “cold stream” applies to third heat flow profile 203 and fifth heat flow profile 205, As used herein, the term “hot stream” applies to first heat flow profile 201, second heat flow profile 202, and fourth heat flow profile 204.

The sum of the enthalpies at each temperature for the cold streams minus the sum of enthalpies at each temperature for the hot streams divided by the sum of the enthalpies at each temperature for the cold streams is defined as the “irreversible thermal losses” of the heat exchange system.

The instant system is designed such that the irreversible thermal losses are minimized. As used herein, the term “minimized” is defined as meaning less than 10%, preferably less than 7.5%, more preferably less than 5%.

Turning to FIG. 5, a method of efficient cold recovery from a liquid hydrogen stream 101 is provided. The liquid hydrogen stream 101 is pressurized in a liquid hydrogen pump, thus producing a cold liquid hydrogen stream 102. The cold liquid hydrogen stream 102 is then warmed by indirect heat exchange with a first part 124 of an inlet air stream 107 and compressed cool feed air stream 108 in liquid hydrogen heat exchanger 123, thereby producing a first cool inlet air stream 126, a first branch 115 of a first section of a further cooled feed air stream 141, and a gaseous hydrogen stream 112.

A liquid oxygen stream is pressurized in a liquid oxygen pump, thus producing a pressurized liquid oxygen stream 106. The liquid oxygen stream 106 is then heated by indirect heat exchange with a second part 125 of inlet air stream 107, and a second fraction of compressed cool feed air stream 129, in at least one main heat exchanger 109. This exchange produces a second cool inlet air stream 127, a third portion of further cooled feed air stream 130 and a gaseous oxygen stream 113. The gaseous hydrogen stream 112 and the gaseous oxygen stream 113 then leave the system. In one embodiment, the gaseous hydrogen stream 112 and/or the gaseous oxygen stream 113 are then utilized in an oxygen-hydrogen combustion turbine.

The liquid oxygen stream 106 has a first molar mass flow rate, and the cold liquid hydrogen stream 102 has a second molar flow rate that may be between 1.5 and 2.5 times the first molar mass flow rate. The cold liquid hydrogen stream 102 may have a pressure greater than 13 bara, preferably greater than 40 bara. The liquid oxygen stream 106 may have a pressure greater than 30 bara.

At least a portion of second cool inlet air stream 127 is introduced into a second cold booster 139, thereby producing a second fraction of compressed cool feed air stream 129. At least a portion of first cool inlet air stream 126 is introduced into a first cold booster 114, thereby producing the compressed cool feed air stream 108.

Compressed cool feed air stream 108 is introduced into liquid hydrogen heat exchanger 123, wherein it becomes first fraction of further cooled feed air stream 141. Second fraction 129 is introduced into main heat exchanger 109, wherein it becomes second fraction of further cooled feed air stream 142. At least a first portion 115 of the further cooled feed air stream 141 is introduced into an expander 116, thereby producing a first expanded feed air stream 136. At least a third portion 130 of second section of a further cooled feed air stream 142 is introduced into a second expander 140 thereby producing a second expanded feed air stream 137. The first expanded feed air stream 136 and the second expanded feed air stream 137 are combined and the combined expanded feed air stream 138 enters air separation unit column 119.

In one embodiment of the present invention, the first cold booster 114 and first expander 116 are connected by a common drive shaft. In one embodiment of the present invention, the second cold booster 139 and second expander 140 are connected by a common drive shaft. In one embodiment, excess power is produced by the combined cold booster 114 and expander 116, which is then used to power an electrical generator (not shown), In one embodiment, excess power is produced by the combined second cold booster 139 and second expander 140, which is then used to power an electrical generator (not shown).

A second portion 118 of the first fraction of further cooled feed air stream 141 is further cooled, thereby producing the first portion of cold feed air stream 133. A second portion 131 of the second fraction of further cooled feed air stream 142 is further cooled, thereby producing the second portion of cold feed air stream 134. The first portion of cold feed air stream 133 and the second fraction of further cooled feed air stream 142 are combined and the combined stream 135 enters air separation unit column 119.

Turning to FIGS. 5a and 5b , the heat flow profile of specific pathways though the main heat exchanger 109 and liquid oxygen heat exchanger 123 are defined. A first heat flow profile 201 is defined as both first section of a further cooled feed air stream 141 and second section of a further cooled feed air stream 142. First section of a further cooled feed air stream 141 is the portion of compressed cool feed air stream 108, that has been partially cooled in liquid hydrogen heat exchanger 123, just prior to first branch 115, being removed. Second section of a further cooled feed air stream 142 is the portion of the second fraction of compressed cool feed air stream 129, that has been partially cooled in man heat exchanger 109, just prior to third portion 130, being removed.

A second heat flow profile 202 is defined as both second branch 118 of further cooled feed air stream 142 and fourth portion 131 of further cooled feed air stream 141. Second branch 118 is the portion of the first fraction compressed cool feed air stream 128, that has been further cooled in liquid hydrogen heat exchanger 123, after first branch 115, has been removed. Fourth portion 131 is the portion of the second fraction compressed cool feed air stream 129, that has been further cooled in main heat exchanger 109, after third portion 130, has been removed.

Third heat flow profile 203 is defined as the section of the heat exchanger 109 in which liquid oxygen stream 106 is vaporized and becomes gaseous oxygen stream 113. Fourth heat flow profile 204 is defined as both the section of the heat exchanger 109 in which second part of inlet air stream 125 is cooled and becomes second cool inlet air stream 127; and the section of the liquid hydrogen heat exchanger 123 in which first part of inlet air stream 124 is cooled and becomes first cool inlet air stream 126. Fifth heat flow profile 205 is defined as the section of the liquid oxygen heat exchanger 123 in which liquid hydrogen stream 101 is heated and becomes gaseous hydrogen stream 112.

As used herein, the term “cold stream” applies to third heat flow profile 203 and fifth heat flow profile 205, As used herein, the term “hot stream” applies to first heat flow profile 201, second heat flow profile 202, and fourth heat flow profile 204.

The sum of the enthalpies at each temperature for the cold streams minus the sum of enthalpies at each temperature for the hot streams divided by the sum of the enthalpies at each temperature for the cold streams is defined as the “irreversible thermal losses” of the heat exchange system.

The instant system is designed such that the irreversible thermal losses are minimized. As used herein, the term “minimized” is defined as meaning less than 10%, preferably less than 7.5%, more preferably less than 5%.

It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above. 

What is claimed is:
 1. A method of efficient cold recovery from a liquid hydrogen stream 101, comprising: warming a cold hydrogen stream 102 by indirect heat exchange with a cold feed stream 103 in sub-cooler 104, thereby producing a warmed hydrogen stream 105, further heating the warmed hydrogen stream 105 and a liquid oxygen stream 106 by indirect heat exchange with an inlet air stream 107, and a compressed cool feed air stream 108, in at least one main heat exchanger 109, thereby producing a cool inlet air stream 110, a further cooled feed air stream 111, the cold feed air stream the compressed cool feed air stream 103, a gaseous hydrogen stream 112 and a gaseous oxygen stream 113, wherein at least a portion of the cool inlet air stream 110 is introduced into a cold booster 114, thereby producing the compressed cool feed air stream 108, at least a first portion 115 of the further cooled feed air stream 111 is introduced into an expander 116, thereby producing an expanded feed air stream 117, a second portion 118 of the further cooled feed air stream 111 is further cooled, thereby producing the cold feed air stream 103, and wherein the liquid oxygen stream 106 has a first molar mass flow rate, and the cold liquid hydrogen stream 102 has a second molar flow rate that is between 1.5 and 2.5 times the first molar mass flow rate.
 2. The method of claim 1, wherein the cold liquid hydrogen stream 102 has a pressure greater than 40 bara.
 3. The method of claim 1, wherein the liquid oxygen stream 106 has a pressure greater than 30 bara.
 4. A method of efficient cold recovery from a hydrogen stream 101, comprising: heating a cold hydrogen stream 102 by indirect heat exchange with a first portion of an inlet stream 124 in hydrogen heat exchanger 123, thereby producing a first cool inlet stream 126, and a gaseous hydrogen stream 112, heating a liquid oxygen stream 106 by indirect heat exchange with a second portion of an inlet air stream 125, and a compressed cool feed air stream 108, in at least one main heat exchanger 109, thereby producing a second cool inlet air stream 127, a further cooled feed air stream 111, the cold feed air stream 103, and a gaseous oxygen stream 113, wherein at least a portion of the second cool inlet air stream 127, and at least a portion of the first cool inlet air stream 126 are combined and introduced into a cold booster 114, thereby producing the compressed cool feed air stream 108, at least a first portion 115 of the further cooled feed air stream 111 is introduced into an expander 116, thereby producing an expanded feed air stream 117, a second portion 118 of the further cooled feed air stream 111 is further cooled, thereby producing the cold feed stream 103, and wherein the liquid oxygen stream 106 has a first molar mass flow rate, and the cold hydrogen stream 102 has a second molar flow rate that is between 1.5 and 2.5 times the first molar mass flow rate.
 5. The method of claim 4, wherein the cold hydrogen stream 102 has a pressure greater than 40 bara.
 6. The method of claim 4, wherein the liquid oxygen stream 106 has a pressure greater than 30 barn.
 7. A method of efficient cold recovery from a hydrogen stream 101, comprising: heating a cold hydrogen stream 102 by indirect heat exchange with a first portion 124 of an inlet air stream 107 in liquid hydrogen heat exchanger 123, and a first fraction 128 of compressed cool feed air stream 108, thereby producing a first cool inlet air stream 126, a first branch 115 of a first section of a further cooled feed air stream 141, and a gaseous hydrogen stream 112, heating a liquid oxygen stream 106 by indirect heat exchange with a second portion of an inlet air stream 125, and a second fraction of a compressed cool feed air stream 129, in at least one main heat exchanger 109, thereby producing a second cool inlet air stream 127, a third portion 130 of second section of further cooled feed air stream 142, a second fraction of a compressed cool feed air stream 134, and a gaseous oxygen stream 113, wherein at least a portion of the second cool inlet air stream 127, and at least a portion of the first cool inlet air stream 126 are combined and introduced into a cold booster 114, thereby producing the compressed cool feed air stream 108, at least a first portion 115 of the further cooled feed air stream 141, and at least a third portion 130 of further cooled feed air stream 142 are combined and introduced into an expander 116, thereby producing an expanded feed air stream 117, a second portion 118 of the further cooled feed air stream 141 is further cooled, thereby producing the cold feed air stream 133, a second portion 131 of the further cooled feed air stream 142 is further cooled, thereby producing the cold feed air stream 134, and wherein the liquid oxygen stream 106 has a first molar mass flow rate, and the cold liquid hydrogen stream 102 has a second molar flow rate that is between 1.5 and 2.5 times the first molar mass flow rate.
 8. The method of claim 7, wherein the cold hydrogen stream 102 has a pressure greater than 40 bars.
 9. The method of claim 7, wherein the liquid oxygen stream 106 has a pressure greater than 30 barn. 